Flexible touch screen display

ABSTRACT

A touch sensitive active matrix display device is provided. The device includes a display fabricated on a first flexible substrate, said display having a viewing surface. The device further includes a touch sensitive sensor including a second flexible substrate, under said display. The touch sensor is operated by touching said viewing surface of said display, and said combined display and touch sensitive sensor is flexible.

This invention generally relates to integration of a flexible touchscreen component, for example, using a resistive touch screentechnology, with a flexible display to make a flexible combinationdevice.

There are several technologies known in the prior art for providing asensor for a touch pad or touch screen. Such known technologies includecapacitive technology, surface acoustic wave technology, pressuresensitive technology such as Quantum Tunnelling Composite (QTC)materials and resistive technology. We have previously describedtechniques for fabrication of flexible displays (see, for example, WO2004/070466, WO 2006/059162, WO 2006/056808, WO 2006/061658, all herebyincorporated by reference). Here we are particularly concerned withintegration of a resistive touch screen component with a display mediaand a backplane incorporating a flexible substrate to form a novelflexible resistive touch screen display structure.

FIG. 1, which is taken from US 2004/121599 shows one example of a knownresistive touch screen display (10). This has a substrate (12), firstconductive layer (14), cover sheet (16), second conductive layer (18)and a backing surface (15). The cover sheet includes integralcompressible spacer dots (50) so that when finger (13) presses on thetouch screen a resistive connection is made between the first and secondconductive layers. The touch screen is provided over a display such asen OLED (Organic Light Emitting Diode) flexible flat panel display.

A significant disadvantage with this configuration is a reduction inclarity caused by locating the touch screen component over the displaymedia—the display must be viewed through the touch screen component thussignificantly reducing the optical clarity of the display.

WO 2005/010735 describes one solution to this problem, in which thedisplay module is provided on a front face of the housing of handheldelectronic equipment and access is provided to the rear surface of thedisplay, on which a touch pad is located. The display is fabricated on aflexible conducting foil substrate which is exposed at the back of thedisplay for detecting capacity of coupling between a user's finger andthe substrate. However this arrangement has the significant drawbackthat the display taint be mounted so that access to the rear of thedisplay, on which is mounted the touch screen component, is provided.

A number of documents describe a type of touch sensitive device in whichan LCD screen underlying substrate to provide a touch sensitive display.For examples reference may be made to U.S. Pat. No. 5,623,280, US2001/0022632, U.S. Pat. No. 5,907,375, and WO 2005/078566 (Which alsomentions organic light emitting diode displays). However in thesedocument the displays are not flexible in a conventional same; they aremerely sufficiently thin to allow the slight deformation needed for theoverall touch sensor functionality. Other background material can befound in US 2003/0026971 and in WO 2004/066136.

In general a rigid substrate has been thought essential for properoperation of the touch screen, but there is a need for a truly flexiblecombination device. There has not previously been any description of howsuch a device might be realised. The inventors have, however, devised atechnique for the fabrication of a combined display device and touchsensor which, as a whole, is truly flexible.

According to the present invention there is therefore provided a torchsensitive active matrix display device, the device comprising: a displayfabricated on a first flexible substrate, said display having a viewingsurface; and a touch sensitive sensor comprising a second flexiblesubstrate, under said display; and wherein said touch sensor is operatedby touching said viewing surface of said display; and said combineddisplay and touch sensitive sensor is flexible.

The touch sensitive sensor, which preferably comprises a flexibleresistive type sensor, is mounted on the rear of the flexible substrate,that is on a side of the display opposite the viewing surface. Howeverin addition, further touch screen technology may be used such asnon-pressure sensitive projected capacitive and inductive type sensors.

In embodiments of the invention, because the touch screen component ispositioned below the device structure there is substantially noimpairment of the optical clarity of the display. Moreover a user canoperate the flexible resistive touch screen display device from theupper, viewing side, therefore making the device easier to use than onein which the rear surface of the display is employed as the touch pad,and enabling a wider range of applications for the device.

In embodiments the touch sensitive sensor and the display both have alayered structure and share the flexible substrate. Thus the sensor maybe fabricated on a flexible substrate backplane of the display, or thedisplay backplane, typically comprising an array of thin filmtransistors, may be fabricated on a flexible substrate a the sensor, orthe flexible substrate backplane for the display may be fabricated on aconducting layer of the sensor. In this latter case the conducting layeracts as the flexible substrate, providing physical support for thedisplay backplane.

Typically the resistive touch screen structure comprises first andsecond conducting layers separated by a spacer arrangement, for examplespacer dots composed of beads in an adhesive matrix, dots that areformed by printing or photolithography, or compressible spacer dotsintegrally formed as part of a flexible layer of the sensor along thelines described in US 2004/212599. However because the sensor is behindthe display there is no need for one or both the conducting layers ofthe sensor to be optically transparent, and in embodiments, asubstantially non-transparent conductor may be employed.

As previously mentioned, typically the display includes a backplanecomprising an array of transistors, and in preferred embodiments thestructure is configured so that the backplane is located on (within orsubstantially adjacent) a neutral axis or surface (plane) of thedevice—that is the neutral axis of the device is adjacent or within alayer comprising the array of thin film transistors (TFTs). This reducesthe mechanical strain on the transistors during use of the touchsensitive display device. Alternatively the touch sensor may be on(within, or substantially adjacent) the neutral axis or surface.

In some preferred embodiments the display device comprises any flatpanel display medium including a reflective display medium, for examplean electrophoretic display medium such as electronic paper, as thisfacilitates the use of a non-transparent conducting material in thetouch screen component. However in other embodiments an emissive displaymedium, for example an OLED display medium, may be employed, oralternatively, a transmissive display medium, such as a liquid crystalmedium may be used.

As previously mentioned, preferably the touch sensitive sensor comprisesa mechanical sensor including first and second layers of conductorswhich are electrically connected together in response to mechanicalpressure, in broad terms, a resistive touch screen sensor. In somepreferred embodiments the display comprises an active matrix displayincluding a multilayer electronic structure adapted to solutiondeposition onto a flexible substrate. Typically the display comprises atwo-dimensional array of pixels addressed by row and column electrodes.The two resistive conducting layers of the touch sensor may each beprovided with electrical connections running the lengths of two oppositeedges, the pairs of edges for the two different conducting layers beingat right angles to one another. In this way the relative magnitude ofcurrent flowing into each edge may be used to determine X and Ycoordinates of a contact between the two layers in a conventionalmanner. For example conventional 4, 5, 8 or 9-wire technology may beemployed.

In a further aspect the invention provides a touch sensitive activematrix display device, said device comprising: a display fabricated on aflexible substrate, said display having a viewing surface; and a touchsensitive sensor under said display; and wherein said touch sensor isoperated by touching said viewing surface of said display; and saidactive matrix display includes a multilayer electronic structure adaptedto solution deposition.

In embodiments the multilayer electronic structure comprises an activematrix backplane of the display.

According to a preferred embodiment of the present invention theflexible touch sensitive active matrix display device comprises anactive matrix of organic field-effect transistors (FETs). An organic FETcomprises an active semiconducting layer of a conjugated polymer or asmall conjugated molecule. Preferably, the organic FET also comprises anorganic gate dielectric layer in the form of either a solution processedpolymer dielectric, such as, but not limited to polymethylmethacrylate(PMMA) or polystyrene (PS) or en organic gate dielectric deposited bychemical vapour deposition, such as, but not limited to, parylene.Preferably, the thickness of the organic dielectric layer is selectedwithin the range of 200 nm and 1 μm. If the dielectric layer is thinnerthan 200 nm, a lower device yield is observed, and the devices are moreprone to mechanical damage and shorting caused by the mechanicalpressure exerted on the active matrix when operating the touch sensor.If the dielectric is thicker than 1 μm, the gate capacitance is too lowto achieve the necessary ON-OFF current ratio needed for operation ofthe display. Organic field-effect transistors, in particular organicFETs comprising conjugated polymer semiconductors and organic gatedielectrics have excellent mechanical properties, such that inembodiments they do not significantly degrade when the flexible touchsensitive active matrix display device is repeatedly bent duringoperation. Also, in embodiments the organic FETs do net exhibitdegradation in their performance when mechanical pressure is appliedwith a stylus or another sharp, pointed object to operate the touchscreen. In contrast many inorganic FETs such as conventional amorphousor polycrystalline FETS are prone to mechanical damage and formation ofmicrocracks when mechanical stress is applied to the layers duringoperation and bending of the flexible touch sensitive active matrixdisplay. In contrast, embodiments of the flexible touch sensitive activematrix display device we describe can be bent repeatedly to a radius ofcurvature of less than 5 cm.

To achieve a desired flexibility of the touch sensitive active matrixdisplay the thickness of any of the substrates used for the touch sensorand for the active matrix display is preferably in the range of 10 μm to250 μm, more preferably in the range of 20 μm to 200 μm. If thethickness of any of the substrates is thicker than this range, theflexibility of the device is impaired. If any of the substrates inbetween the viewing surface and the bottom substrate of the touch sensoris thicker than 250 μm the resolution of the touch screen is degraded,since higher mechanical forces are required to transmit the mechanicalpressure from the viewing surface of the display to the touch sensormounted underneath. The thickness of the bottom substrate of the touchsensor can in principle be made thicker than any of the other substratesof the device, without it significantly affecting the operation of thetouch screen. However, the thickness of the bottom substrate of thetouch sensor may be limited by the overall bending requirements for thedevice.

Preferably the active matrix array of FETs is located near the neutralaxis of the device, and in order to achieve this, the thickness of thebottom substrate should not be significantly larger than the othersubstrates of the device. Let d₁ be the thickness of the flexiblesubstrate between the display medium/active matrix and the viewingsurface of the device, d₂ the thickness of the flexible substrate onwhich the active matrix is formed, and d₃ and d₄ the thickness of anupper and lower flexible substrate of the touch sensor, respectively. Inone embodiment of the invention the substrate of the active matrix andthe upper flexible substrate of the touch sensor are glued together witha pressure sensitive adhesive. Assuming that the thickness of thevarious active layers of the active matrix, the display medium and thetouch sensor are small compared with that of any of the substrates, thenin some embodiments d₂+d₃+d₄≈d₁.

Alternatively, the neutral axis of the device may be selected to be inthe plane of the touch sensor elements. In the ease of a resistive touchsensor large stress due to bending can lead to erroneous signals fromthe touch sensor since bending can lead to the two sensing electrodestouching in the absence of mechanical input. This can be minimized byplacing the touch sensor element in the neutral axis. Thus in some otherembodiments d₄≈d₁+d₂+d₃.

In another aspect the invention provides a touch sensitive displaydevice, said device comprising: a display fabricated on a flexiblesubstrate, said displaying having a viewing surface; and a touchsensitive sensor under said display; and wherein said touch sensor isoperated by touching said viewing surface of said display; and saidtouch sensitive sensor is pixellated.

The skilled person will appreciate that features from theabove-described aspects and embodiments of the above-described aspectsof the invention may be combined in any permutation.

In a still further aspect the invention provides use of a touchsensitive display device as described above, the use comprising:displaying an image on the display device, and sensing touching of theviewing surface of the display and providing a touch sensing signal.

Accordingly, one embodiment of the present invention provides a deviceconfiguration for a resistive touch screen structure which incorporatesa flexible display medium in contact with a flexible backplane. Thebackplane comprises an active matrix array of transistors and is formedon a flexible substrate. The flexible display medium is brought incontact with the flexible backplane either through direct deposition ofa display active layer, such as an organic light-emitting diode orliquid-crystal display cell, or through lamination with a displaymedium, such as, but not limited to, an electrophoretic, electrochromicor electronic paper display medium on flexible countersubstrate. Thedisplay comprising the flexible backplane and the flexible displaymedium is laminated on top of a resistive touch screen sensor, which isoperable from the top by applying pressure to the display media. Bylocating the touch screen sensor behind the flexible display the opticalquality of the display is not impaired by the finite optical absorptionand reflection of the metallic and dielectric layers of the touch screensensor. In embodiments no optical design compromise, or opticalengineering of the display or the touch screen is necessary to integratethe touchscreen functionality with the display.

Embodiments allow incorporation of a non-transparent conductor materialwithin the resistive touch screen component. Such a material could be athin metallic layer, which replaces the conventional transparentmaterial, such as ITO, of the conductive layers. The use of ITO or otherequally brittle materials is not preferred for incorporation into aflexible display, where such materials could be subject to cracking uponflexing. The main advantages of using ITO in current touch screentechnology are the fact that ITO is highly conductive, but also highlytransparent and is therefore a useful material to ensure the highestdegree of optical clarity possible, for the user. The need fortransparent materials is described in the prior art as beingparticularly important. However, the cost of ITO coatings issignificant, and this is expected to increase in the future due toscarce natural resources of the raw materials, in particular indium. Inembodiments of the invention there is no need to use a transparentconductor for realizing the touch screen functionality, and any metalsuitable for flexible substrate integration, such as a conductingpolymer or a low-cost, thin-film vacuum or solution-deposited inorganicmetal, such as copper or aluminium can be employed.

In a further embodiment the thickness of the overall touch screenstructure of the device configuration may be reduced by eliminating theneed for an upper polymer film. In this configuration the upperconductive layer of the touch screen is deposited directly onto thebottom surface of the flexible backplane.

In another embodiment, the backplane is processed directly onto theupper conductive layer of the resistive touch screen component. Thisdevice design eliminates the need for a separate substrate to be usedfor the backplane but instead the transistors are fabricated onto theupper conductive layer of the touch screen component.

To help understanding of the invention, a specific embodiment thereofwill now be described by way of example and with reference to theaccompanying drawings, in which:

FIG. 1 illustrates a touch screen structure configuration known in theart;

FIG. 2 illustrates a device configuration for a resistive touch screenstructure incorporating the touch screen component underneath a flexibledisplay according to an embodiment of the present invention;

FIG. 3 shows the elements of a resistive touch screen component that isincorporated underneath the resistive touch screen device structure;

FIG. 4 shows the elements of a resistive touch screen component that isincorporated underneath a flexible display wherein the upper electrodeof the touch screen sensor is deposited onto the back of the substrateof the flexible display according to the present invention.

FIG. 5 shows the elements of a resistive touch screen component that isincorporated underneath a flexible display the flexible displaybackplane is processed directly onto the touch screen component;

FIG. 6 illustrates a thin film transistor and a flexible substrate; andcross-sectional and plan views respectively of an active matrix displaydevice suitable for solution deposition.

Broadly speaking we will describe a flexible display device with anintegrated touch sensor, wherein a resistive touch screen component isplaced underneath a flexible display without impairing the opticalclarity of the display, hence yielding 100% optical clarity. Theflexible display incorporates a flexible display medium in contact witha flexible backplane on a flexible substrate that allows for the deviceto be operable from the top by applying pressure to the display media.The flexible display medium and the display backplane are laminated overthe resistive touch screen component.

Referring to the drawings, FIG. 2 illustrates a device configuration fora resistive touch screen structure which incorporates a display media101, laminated over a flexible backplane 102. The display mediapreferably has ultra thin dimensions as described further later.Preferably, an electrophoretic display media is incorporated within thedevice structure and is located over the backplane. The backplaneincorporates a flexible substrate 102 b as is shown in FIG. 2. Theflexible substrate 102 b may be either a thin layer of glass, polymide(PI) or a flexible metallic foil, but preferably the flexible substrateconsists of a polymer film, such as polyethyleneterephtalate (PET) orpolyethylenenaphtalene (PEN). The display media 101 and displaybackplane 102 are then laminated over a resistive touch screen 103 byutilising a pressure sensitive adhesive (PSA).

Optical clarity is achieved by incorporating a touch screen componentonto the backside of the flexible display. FIG. 3 illustrates theelements of a resistive touch screen component 103 that is located onthe underneath side of the device. A conducting lower layer 107 isdeposited over a bottom substrate 108. The bottom substrate 108 ispreferably also is flexible substrate, such as polyethyleneterephtalate(PET) or polyethylenenaphtalene (PEN). Generally, the choice of thebottom substrate 108 is less critical for the operation of the touchscreen than of the other substrate below (see discussion below).

A layer of insulating spacer dots 106 is positioned over the lowerconductor layer, followed by a further upper layer of conductingmaterial 105, which may be of the same material as the lower layer ofconductor material. The spacer dots are positioned in between theconductive layers, in order to separate the said lower and upperconductor layers 105, 107. An upper flexible substrate film 104, suchas, but not limited to a plastic substrate, such as PET or PEN, a thinmetal foil substrate, such as steel, or a thin glass substrate completesthe resistive touch screen component, by forming the upper substrate ofthe said component. A preferred thickness of the upper substratematerial is between 25 μm-50 μm in order to achieve optimum sensitivityof the touchscreen to local pressure applied from the top.

In embodiment of the present invention, the conductive layers 105, 107of the touch semen can be fabricated from either transparent conductorssuch as ITO, or non-transparent conductor material, such as a thinmetallic layer. In contrast to a device structure where the resistivetouch screen is located on top of the display, i.e. in between the userand the display medium, the configuration described here, where thetouch screen is hidden from the user behind the display does not requirethe touch screen to be transparent. Thus, cheap, non-transparent metalssuch as copper or aluminium can be used for the electrode of the touchscreen. Within this novel device configuration, the ability to use anon-transparent conductive material can be used to increase theflexibility of the resistive touch screen device, as thin films ofductile metals are often more flexible than the use of a brittle ceramicsuch as ITO. In addition, the use of metallic materials for theconductive layers will also have the effect of reducing costs, as thinfilms of metallic material are generally cheaper materials than ITO. Inaddition, the effects of the use of metallic layers may also be seen ingeneral performance improvements within the touch screen component, dueto the fact that higher conductivity levels may be achieved withmetallic materials than with ITO.

To achieve good sensitivity of the touch screen to applied pressure fromthe top, the upper substrate of the touch semen 104, and the substrateof the flexible backplane 102 b, as well as the display medium 101should be as thin as possible, while maintaining sufficient mechanicalintegrity and rigidity during manufacture as well as operation.Preferably the thickness of these substrates is on the order of 10-250μm, more preferably on the order of 20-200 μm. A particularly preferredthickness is approximately 175 μm.

The prevent configuration of the resistive touch screen device allowsfor the alteration of the thicknesses of the various layers of the wholedevice stack, in particular the thicknesses of the substrates 108, 104,102 b, and of the display medium and its support in order to ensure thatthe backplane of the display, comprising an array of thin-filmtransistors of the device is located in the neutral axis of the device.By locating the transistors within this neutral axis, this ensures thata minimum stress is applied to the backplane upon flexing the resistivetouch screen device. Alternatively, the neutral axis of the device canbe designed to lie within another layer of the structure which is mostprone to mechanical damage, fracture or delamination during flexing.

In embodiments of the present invention, the thickness of the overalltouch screen structure of the novel device configuration may be reducedby eliminating the need for an upper substrate 104 of the touch screen.In this configuration the upper conductive layer 105 of the resistivetouch screen is deposited onto the bottom surface of the flexiblebackplane 102 b (see FIG. 4). This can be achieved by patterning a setof conducting electrodes and interconnects onto the bottom of substrate102 b as part of the manufacturing steps for the flexible backplane, andthen subsequently, laminating the flexible backplane with the bottomsubstrate 108 of the touch screen using similar lamination processes ascurrently used for bringing in contact the upper and lower substrates108, and 104 of a conventional touch screen. Alternatively, it ispossible to fabricate the flexible backplane directly on top of theupper substrate 104 of the touch screen, by using a completed touchscreen laminate as the substrate in the manufacturing process of theactive matrix transistor array.

To further reduce the overall thickness of the device, the flexiblebackplane 102 comprising the transistors of the device, may be processeddirectly onto the upper conductive layer of the resistive touch screencomponent, as is shown in FIG. 5. To provide electrical insulation athin dielectric isolation layer 109 is deposited in between the upperconductive layer 105 of the touch screen, and the electroactive layersof the flexible backplane. This isolation layer has a thickness ofpreferably on the order of 1-20 μm. It can also be used to provideplanarization of the surface of the touch screen. In this way the needfor a separate substrate to support the backplane is eliminatedresulting in a further improvement of the sensitivity of the touchscreen to pressure applied through the display element.

In a preferred embodiment of the present invention, a backplane 102 ofthe resistive touch screen display device is formed on the top side ofthe resistive touch screen component 103. The complete display isfabricated using an active matrix driving arrangement.

The said backplane comprises an array of transistors. An exampletransistor is shown in FIG. 6. In some preferred embodiments of thepresent invention each transistor that forms an array of transistorsincorporated onto the backplane may be produced by the following method:conductive material is deposited and patterned on a substrate 110 toform source and drain electrodes 111, 112. Preferably, a flexiblesubstrate may be used that is composed of either glass or a polymerfilm, but preferably a plastic substrate 102 b such aspolyethyleneterephtalate (PET) or polyethylenenaphtalene (PEN) is used.The patterned conductive layer 111, 112 comprises a conducting polymer,such as PEDOT, or a metallic material, such as gold or silver. It may bedeposited and patterned through solution processing techniques such as,but not limited to, spin, dip, blade, bar, slot-die, or spray coating,inkjet, gravure, offset or screen printing. Alternatively, vacuumdeposition techniques may be used, such as evaporation and sputtering aswell as photography techniques.

Once the conductive layer has been patterned to form the source anddrain electrodes, a layer of semiconducting material 113 may then bedeposited over the substrate and patterned electrodes. Thesemiconducting layer may comprise a vacuum or solution processibleorganic or inorganics semiconducting material, such as, but not limitedto semiconducting polymers, such as polyarylamine, polyfluorene orpolythiophene derivatives, a small molecule organic semiconductor, suchas pantacene, or a solution-processible inorganic material, such asCdSe, ZnO, or silicon based-nanowires. A broad range of printingtechniques may be used to deposit the semiconducting material including,but not limited to, inkjet printing, soft lithographic printing (J. A.Rogers et al., Appl. Phys. Lett. 75, 1010 (1999); S. Brittain et al.,Physics World May 1998, p. 31), screen printing (Z. Bao, et al., Chem.Mat. 9, 12999 (1997)), offset printing, blade coating or dip coating,curtain coating, meniscus coating, spray coating, or extrusion coating.Alternatively, the semiconducting layer may be deposited as a thincontinuous film and patterned subtractively by techniques snout saphotolithography (see WO 99/10939) or laser ablation.

A layer of gate dielectric material 114 is then deposited onto thelayered substrate. Materials such as polyisobutylene or polyvinylphenolmay be used as the dielectric material, but preferablypolymethylmethacrylate (PMMA) and polystyrene are used. The dielectricmaterial may be deposited in the form of a continuous layer, bytechniques such as, but not limited to, spray or blade coating. However,preferably, the technique of spray coating is used.

The deposition of the dielectric layer is then followed by thedeposition of a gate electrode 115 and interconnect lines. The materialof the gate electrode may be a thin film of inorganic metal such as goldor a cheaper metal such as copper or Aluminium. The gate electrode isdeposited using techniques such as sputtering or evaporation techniquesor solution processing techniques such as spin, dip, blade, bar,slot-die, gravure, offset or screen printing. Alternatively, electrolessdeposition techniques or laser ablation may be used.

The transistors are fabricated in the form of an active matrix arraywith data, gate addressing as well as common electrodes. Each pixel ofthe array may contain one or more transistors. At least one of theelectrodes of the transistors is coupled to an electroactive displayelement, such as, but not limited to an electrophoretic, electrochromic,or electronic paper display pixel, a liquid crystal display pixel, or anorganic light-emitting diode to control the state of the display elementby applying either a voltage or current to the display element. Thedisplay medium is preferably a reflective display medium in order tofacilitate use of non-transparent metals for the touch screen component.However, the display medium can also be a transmissive medium in whichcase the touch screen is fabricated from transparent conductors, such asITO.

Finally, a display media component 1 is attached to the completedbackplane and the underlying resistive touch screen structure. Thedisplay medium is either deposited directly onto the flexible backplanesubstrate. For example, in the case of a top-emitting polymerlight-omitting display medium the optically active polymers can beinkjet printed into the pixel locations of the active matrix followed bydeposition of a transparent top cathode, and a transparent encapsulationlayer. In the ease of an electrophoretic display medium a film ofelectrophoretic ink deposited onto a top substrate with a transparentconductive electrode is laminated with the flexible backplane.

FIGS. 7 a and 7 b, which are taken from the Applicant's WO 2004/070466,show cross-sectional and top views of an active matrix pixel where thedisplay media is voltage controlled, such as liquid crystal orelectronic paper. FIG. 7 a shows a side view of a transistor-controlleddisplay device including a pixel capacitor. It has a substrate 701, asemiconductor 702, which may be a continuous layer or may be patterned,(in the figure the semiconductor is patterned to cover the transistorchannel), a data line 703, a pixel electrode 704, a transistordielectric 705, a gate electrode/gate interconnect 706 and a displaymedia 707 (for example liquid crystal or electronic paper and a counterelectrode 708 of the display media. In this example the state of thedisplay media is determined by the electric field across the media, anda switchable area 709 of the device can be switched by a voltagedifference between the pixel 704 and the top electrode 708.

Although WO 2004/070466 describes fabrication of the display on a rigidsubstrate using solution deposition techniques (such as inkjet printing,screen printing and offset printing), as described above a similardisplay can be fabricated on a flexible substrate such as a plasticsubstrate, also using solution deposition techniques. Some furtherpreferred aspects of solution deposition techniques for deposition ontoa flexible substrate are described in the applicant's co-pending UKpatent applications nos. 0570173.8, 0506613.9, and 0511117.4, amongothers, the contents of which are hereby incorporated by reference.

When the flexible display is brought in contact with the touch screenthe two components should be registered with respect to each other inorder to ensure that applying pressure to a defined area of the displaydevice, activates the correct region of the touch screen. This can beachieved by optical alignment prior to lamination of the two components.In the case of a fabrication process, where at least one of the layersof the flexible backplane and of the touch screen are deposited onto thesame substrate the layers of the touch screen and of the flexiblebackplane can be aligned with respect to each other during thepatterning of these layers.

The present invention is not limited to the foregoing examples. Forexample, although the use of a resistive touch sensor has been describedother touch sensitive technology such as that mentioned in theintroduction, may also be employed.

Aspects of the present invention include all novel and/or inventiveaspects of the concepts described herein and all novel and/or inventivecombinations of the features described herein. The applicant herebydiscloses in isolation each individual feature described herein and anycombination of two or more such features, to the extent that suchfeatures or combinations are capable of being carried out based on thepresent specification as a whole in the light of the common generalknowledge of a person skilled in the art, irrespective of whether suchfeatures or combinations of features solve any problems disclosedherein, and without limitation to the scope of the claims. Aspects ofthe present invention may comprise any such individual feature orcombination of features. In view of the foregoing description it will beevident to a person skilled in the art that various modifications may bemade within the scope of the invention.

1. A touch sensitive active matrix display device, the devicecomprising: a display fabricated on a first flexible substrate, saiddisplay having a viewing surface; and a touch sensitive sensorcomprising a second flexible substrate, under said display; and whereinsaid touch sensor is operated by touching said viewing surface of saiddisplay; and said combined display and touch sensitive sensor isflexible.
 2. A touch sensitive display device as claimed in claim 1wherein said first and second flexible substrates comprise a sharedflexible substrate.
 3. A touch sensitive display device as claimed inclaim 2 wherein said shared flexible substrate comprises a backplane ofsaid display.
 4. A touch sensitive display device as claimed in claim 3wherein a conductive layer of said touch sensor is fabricated on saidbackplane.
 5. A touch sensitive display device as claimed in claim 2wherein said shared flexible substrate comprises a touch screenlaminate, and wherein a backplane of said display is fabricated on saidlaminate.
 6. A touch sensitive display device as claimed in claim 1wherein said touch sensitive sensor and said display each have a layeredstructure, and wherein said display comprises at least one layer of saidtouch sensitive sensor, whereby said display and said sensor have atleast one of said layers in common.
 7. A touch sensitive display deviceas claimed in claim 6 wherein said first flexible substrate of saiddisplay comprises said second flexible substrate of said touch sensitivesensor.
 8. A touch sensitive display device as claimed in claim 6,wherein said first flexible substrate is positioned directly over aconductor layer of said touch sensitive sensor.
 9. A touch sensitivedisplay device as claimed in claim 6 wherein said first flexiblesubstrate of said display comprises a backplane fabricated on aconductor layer of said touch sensitive sensor.
 10. A touch sensitivedisplay device as claimed in claim 1 wherein said touch sensitive sensorincludes a layer comprising a substantially non-transparent conductor.11. A touch sensitive display device as claimed in claim 1 wherein saiddisplay includes a backplane comprising an array of thin-filmtransistors, and wherein said backplane is located substantially on aneutral surface of said device.
 12. A touch sensitive display device asclaimed in claim 1 wherein said display comprises a pixellated display.13. A touch sensitive display device as claimed in claim 1 wherein saidtouch sensitive display device is pixellated.
 14. A touch sensitivedisplay device as claimed in claim 1 wherein said display devicecomprises a reflective display medium.
 15. A touch sensitive displaydevice as claimed in claim 14 wherein said reflective display mediumcomprises an electrophoretic display medium.
 16. A touch sensitivedisplay device as claimed in claim 1 wherein said touch sensitive sensorcomprises a mechanical sensor including first and second conductinglayers separated by an insulating spacer layer and configured to bringsaid first and second conducting layers into contact with one another toelectrically connect said first and second conducting layers ofconductors in response to mechanical pressure.
 17. A touch sensitivedisplay device as claimed in claim 1 wherein said display includes amultilayer electronic structure adapted to solution deposition.
 18. Atouch sensitive display device as claimed in claim 17 wherein saidmultilayer electronic structure comprises an active matrix backplane ofsaid display.
 19. A touch sensitive active matrix display device asclaimed in claim 1, wherein said active matrix comprises an array offield-effect transistors comprising an organic semiconductor.
 20. Atouch sensitive active matrix display device as claimed in claim 19,wherein said organic semiconductor is a solution-processed polymersemiconductor.
 21. A touch sensitive active matrix display device asclaimed in claim 19, wherein said field-effect transistor comprises anorganic gate dielectric.
 22. A touch sensitive active matrix displaydevice as claimed in claim 21, wherein said organic gate dielectric is asolution-processed polymer dielectric.
 23. A touch sensitive activematrix display device as claimed in claim 21, wherein said organic gatedielectric is deposited by chemical vapour deposition.
 24. A touchsensitive active matrix display device as claimed in claim 23, wheresaid organic gate dielectric is parylene.
 25. A touch sensitive activematrix display device as claimed in claim 21, wherein said organic gatedielectric has a thickness between 200 nm and 1 μm.
 26. A touchsensitive active matrix display device as claimed in claim 1, whereinsaid touch sensitive sensor is a resistive touch sensor.
 27. A touchsensitive display device as claimed in claim 1 wherein one or both ofsaid first and second flexible substrates has a thickness in the rangeof 10 μm to 250 μm.
 28. A touch sensitive display device as claimed inclaim 1 wherein one or both of said first and second flexible substrateshas a thickness in the range 20 μm to 200 μm.
 29. A touch sensitiveactive matrix display device, said device comprising: a displayfabricated on a flexible substrate, said display having a viewingsurface; and a touch sensitive sensor under said display; and whereinsaid touch sensor is operated by touching said viewing surface of saiddisplay; and said active matrix display includes a multilayer electronicstructure adapted to solution deposition.
 30. A touch sensitive activematrix display device as claimed in claim 29, wherein said active matrixcomprises an array of field-effect transistors comprising an organicsemiconductor.
 31. A touch sensitive active matrix display device asclaimed in claim 30, wherein said organic semiconductor is asolution-processed polymer semiconductor.
 32. A touch sensitive activematrix display device as claimed in claim 29, wherein said field-effecttransistor comprises an organic gate dielectric.
 33. A touch sensitiveactive matrix display device as claimed in claim 32, wherein saidorganic gate dielectric is a solution-processed polymer dielectric. 34.A touch sensitive active matrix display device as claimed in claim 32,wherein said organic gate dielectric is deposited by chemical vapourdeposition.
 35. A touch sensitive active matrix display device asclaimed in claim 34, where said organic gate dielectric is parylene. 36.A touch sensitive active matrix display device as claimed in claim 32,wherein said organic gate dielectric has a thickness between 200 μm and1 μm.
 37. A touch sensitive active matrix display device as claimed inclaim 29, wherein said touch sensitive sensor is a resistive touchsensor.
 38. A touch sensitive display device, said device comprising: adisplay fabricated on a flexible substrate, said displaying having aviewing surface; and a touch sensitive sensor under said display; andwherein said touch sensor is operated by touching said viewing surfaceof said display; and said touch sensitive sensor is pixellated.